While using this component I got an error SEVERE: java.lang.NoClassDefFoun

Directory Graph Explorer (Vaadin 7)
1

While using this component I got an error
SEVERE:
java.lang.NoClassDefFoundError: org/apache/commons/collections15/Transformer
at com.vaadin.graph.GraphExplorer.(GraphExplorer.java:62)

I am using Vaadin 8.4.5, JDK 8.
Any idea ?

2

You probably have two transient dependencies to org.apache.commons.collections in the project, with different version, which produces conflict. So class loader cannot load the class. You should run mvn dependency:tree to verify this. If you find two versions, the other one needs to be excluded.